The artificial milk made from soybeans, hereafter called soymilk, is well recognised to be a highly nutritious, versatile and economical food. However, most methods of making soymilk develop unacceptable off-flavors which greatly limit its use.
Plant protein in legumes and oilseeds, such as cottonseed, peanut, rapeseed, saflower, sesame, soybean and sunflower, is of high enough quality to be almost nutritionally equivalent to the animal protein at a fraction of the cost of the latter. The processing of these seeds to make protein foods having high solubility in water usually leads to flavor and taste problems. Such problems have limited their use mainly for edible oil extraction. The protein rich seed meal remaining after extraction of oil is used essentially as animal feed.
It is well known that certain enzymes present in soybeans and many other seeds are the major cause of off-flavors arising upon processing these seeds for foods. Polyunsaturated fatty acids are catalytically oxidized by the enzymes in the presence of water and oxygen to produce hydroperoxides which finally yield the off-flavor causing volatiles. Lipoxygenase, distributed throughout the soybean cotyledons, becomes active as soon as their cell structure is broken. Therefore, the control of off-flavors has traditionally been done by inactivating the enzyme, such as by heating and/or altering pH of the aqueous medium in which the seeds are disintegrated. The problem with these treatments has been that they tend to insolublize the soybean protein and thereby reduce soymilk yield and make it chalky in mouthfeel. The degree of enzyme inactivation required to reduce the off-flavors to acceptable level leads to an unacceptably low protein solubility. An approach of tackling the problem is to only partially inactivate the enzyme, remove most remaining off-flavor by deodorization, and mask any residual off-flavor by flavoring. In another approach, the enzyme is totally inactivated prior to disintegrating the beans, and the resulting insoluble soybean protein is dispersed in water by fine grinding and high pressure homogenizing. Yet another approach has been to inactivate the enzyme partially by grinding the beans in hot, pH controlled aqueous medium under limiting oxygen condition. Existing methods of making no-beany flavor soymilk are based on the above approaches or a combination of these.
Only recently was it recognized and demonstrated that it is totally unnecessary to inactivate the enzyme, prior to or during the disintegration of soybeans, if said disintegration is carried out in an oxygen-free environment. This method has yielded soymilk with absolutely no beany flavor, high degree of dissolved proteins and other soybean solids and no bitterness or throat catching sensation. Employing this method, the present invention describes an equipment to make soymilk, and aqueous extract of other seeds having problems similar to that of soybeans, in commercial as well as small quantities.